| 摘要 |
Light-fast coating materials (I), consisting of cosolvent- free, aqueous, anionic dispersions of polyurethane-polyureas (PUR), in which the solid component contains the reaction product (at least partly in salt form) of (a) an NCO prepolymer derived from (i) 20-60 wt% aliphatic and/or cycloaliphatic di-isocyanate, (ii) 20-60 wt% macrodiol(s) with a mol. wt. of 500-10,000, (iii) 2-12 wt% 2,2-bis-hydroxymethyl-mono-alkanoic acid, preferably dimethylolpropionic acid (DMPA), (iv) 0-15 wt% short-chain diols with a mol. wt. of 62-400 and (v) 0-10 wt% monofunctional alcohols with a mol. wt., of 32-350 as chain regulators, (b) 0-15 wt% diamines with a mol. wt. of 60-300 as chain extenders, (c) 0-10 wt% monoamine, alkanolamine or ammonia as chain regulators, (d) 0-3 wt% water and (e) 0.1-10 wt% neutralising agent. The reaction in the prepolymer stage (a) is taken to 65-85 (preferably 75-80) % of the calculated NCO content. Also claimed is (1) a process for the production of (I) as above, in which stage (a) is carried out at 5-150 (preferably 50-110) degrees C in presence of inert solvent with a boiling range of 50-100 degrees C, preferably acetone, the amount of water added (d) is 0-30 wt% based on solids, more water is added with the neutralising agent (e), and the solvent is removed after the reaction by distillation, optionally under reduced pressure; (2) waterproof, transparent coatings of (I) which are resistant to tearing, UV, temperature and organic or inorganic deposits, show good adhesion to substrates and are easily stripped off when required; (3) a process for recycling used, stripped coatings of paint (I), by optionally cleaning, mechanically pulverising, dissolving (optionally with heating) in acetone, water and neutralising agent (preferably ammonia), and distilling off the acetone under reduced pressure to give a reusable aqueous dispersion of (I). |
